Here's why:
* Barium sulfate (BaSO₄) is a sparingly soluble ionic compound. This means it dissolves to a small extent, forming barium ions (Ba²⁺) and sulfate ions (SO₄²⁻) in solution.
* Sodium sulfate (Na₂SO₄) is a soluble ionic compound that fully dissociates in solution, producing sodium ions (Na⁺) and sulfate ions (SO₄²⁻).
* Common ion effect: When you add sodium sulfate to the barium sulfate solution, you are introducing additional sulfate ions. This increases the concentration of sulfate ions in the solution. According to Le Chatelier's principle, the equilibrium of the dissolution of barium sulfate will shift to the left, causing more barium sulfate to precipitate out of solution.
Therefore, the common ion in this scenario is sulfate (SO₄²⁻).
